Administering an injection is a process which presents a number of risks and challenges for users and healthcare professionals, both mental and physical.
Injection devices (i.e. devices capable of delivering medicaments from a medication container) typically fall into two categories—manual devices and auto-injectors.
In a manual device—the user must provide the mechanical energy to drive the fluid through the needle. This is typically done by some form of button/plunger that has to be continuously pressed by the user during the injection. There are numerous disadvantages to the user from this approach. If the user stops pressing the button/plunger then the injection will also stop. This means that the user can deliver an underdose if the device is not used properly (i.e. the plunger is not fully pressed to its end position). Injection forces may be too high for the user, in particular if the patient is elderly or has dexterity problems.
The extension of the button/plunger may be too great. Thus it can be inconvenient for the user to reach a fully extended button. The combination of injection force and button extension can cause trembling/shaking of the hand which in turn increases discomfort as the inserted needle moves.
Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc.
Auto-injectors are devices which completely or partially replace activities involved in parenteral drug delivery from standard syringes. These activities may include removal of a protective syringe cap, insertion of a needle into a patient's skin, injection of the medicament, removal of the needle, shielding of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Forces required of the user/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button, the action of placing the autoinjector against the skin, or the action of the needle reaching its injection depth. In some devices the energy to deliver the fluid is provided by a spring.
Auto-injectors may be disposable or single use devices which may only be used to deliver one dose of medicament and which have to be disposed of after use. Other types of auto-injectors may be reusable. Usually they are arranged to allow a user to load and unload a standard syringe. The reusable auto-injector may be used to perform multiple parenteral drug deliveries, whereas the syringe is disposed after having been spent and unloaded from the auto-injector. The syringe may be packaged with additional parts to provide additional functionality.
US 2002/0095120 A1 discloses an automatic injection device which automatically injects a pre-measured quantity of fluid medicine when a tension spring is released. The tension spring moves an ampoule and the injection needle from a storage position to a deployed position when it is released. The content of the ampoule is thereafter expelled by the tension spring forcing a piston forward inside the ampoule. After the fluid medicine has been injected, energy stored in the tension spring is released and the injection needle is automatically retracted back to its original storage position.
WO 2009/153542 A1 discloses an injection device comprising a housing adapted to receive a syringe having a discharge nozzle, the syringe being moveable in the housing on actuation of the injection device along a longitudinal axis from a retracted position in which the discharge nozzle is contained within the housing and an extended position in which the discharge nozzle of the syringe extends from the housing through an exit aperture. There is an actuator and a drive adapted to be acted upon by the actuator and in turn act upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle. A locking mechanism is moveable from an engaged position in a direction into the housing at the exit aperture into a disengaged position. The locking mechanism is adapted to prevent actuation of the device when it is in its engaged position and permit actuation of the device when it is in its disengaged position. The exit aperture is defined by a rim located on an edge of the housing and the locking mechanism comprises a contact surface which is adapted to extend over or around at least a part of the rim.
WO 2008/093063 A2 discloses an auto injector including: a housing; an outlet portion with a needle moveable relative to the housing; a container within the housing for containing medicament; and an actuatable deployment mechanism configured to deploy the outlet portion by moving the outlet portion relative to the housing and to eject medicament contained in the container through the outlet portion. The auto injector is configured to store a volume of fluid and includes a filling mechanism configured to expel the volume of fluid from the outlet portion and subsequently to draw medicament through the outlet portion and into the container. An adaptor fits to the auto injector so as to cover the needle and includes a puncture member configured to puncture a vial, the puncture member providing fluid communication to the needle. The auto injector and adaptor are provided as part of an auto injector pack together with a vial containing a substance which in combination with the liquid forms the medicament and a casing configured to house the vial, the auto injector and the adaptor.
U.S. Pat. No. 6,575,939 discloses a single-use device for injecting a dose of a medicinal product, comprising a syringe and a piston rod provided with a collar housed in a casing formed of two parts, a front part and a rear part, fitted inside each other and capable of sliding in relation to each other over a short traverse between two positions, a retracted position and a forward position. This device additionally includes means for supporting the collar of the piston rod arranged so as to permit, on the one hand, injection under the effect of a propulsion spring in the forward position of the parts of the casing and, on the other hand, backward movement of the syringe inside the casing, after injection, in the retracted position of the said parts of the casing. It also includes means for viewing the supporting means at the end of injection.
In order to prevent needle stick injuries due to inadvertently operated auto-injectors it is desirable to prevent the trigger button from being pressed as long as the auto-injector is not properly positioned against an injection site, i.e. a user's skin.